This invention relates generally to an improved gear train for a timepiece with an electric stepping motor. More particularly, the invention relates to an overhung gear train assembled from one side of the watch frame and having improvements in the arrangement of wheels and the journal bearing supports.
Electronic timepieces of the "analog" type, i.e., having conventional rotating hands have been developed wherein a stepping motor is accurately driven from a time based electrical driving signal. The driving signal may come from a transistor pulse-producing circuit, or more recently, from an integrated circuit having a quartz oscillator time base.
Since a stepping motor may be rotatably advanced at any desired pulse frequency, this leads to opportunities in reducing the number of components in the conventional gear train from those in a continuous rotating synchronous driving motor. An example of a quartz oscillator controlled stepping motor driven periodically by pulses and directly geared to the sweep seconds wheel on the main arbor is shown in U.S. Pat. No. 3,824,781 in the name of G. Diersbock issued July 23, 1974 and assigned to the present assignee. Placement of a gear train on "overhung" arbors, defined herein as arbors journaled on only one end, as opposed to being journaled on both ends between two spaced frame plates, has been suggested in the prior art, such as U.S. Pat. No. 4,079,582--Tamuru et. al. issued March 31, Tamuru In the Tamaru patent, the stepping motor drives the gear train through a frictionally coupled toothed claw.
A gear train mounted on overhung arbors rotating in a single journal is less stable than one mounted between two frame plates and is subject to wobble or misalignment unless measures are taken to provide a rigid journal mounting. However, a great advantage of an overhung gear train is that it lends itself to automated assembly of the timepiece from one side of the frame.
Accordingly, one object of the present invention is to provide an improved overhung gear train assembly for a stepping motor timepiece.
Another object of the invention is to provide an improved arrangement for a stepping motor timepiece which facilitates automated assembly processes.